Overview of Environmental and Hydrogeologic Conditions at Merrill Field Airport, Anchorage, Alaska By Allan S. Nakanishi U.S. GEOLOGICAL SURVEY Open-File Report 95-171 Prepared in cooperation with the FEDERAL AVIATION ADMINISTRATION Anchorage, Alaska 1995 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director For additional information write to: Copies of this report may be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Earth Science Information Center 4230 University Drive, Suite 201 Open-File Reports Section Anchorage, AK 99508-4664 BOX25286, MS 517 Federal Center Denver, CO 80225-0425 CONTENTS Abstract ................................................................. 1 Introduction............................................................... 1 Background............................................................... 1 Location and history .................................................... 1 Merrill Field FAA facilities............................................... 3 Physical setting ............................................................ 3 Climate .............................................................. 3 Vegetation............................................................ 3 Geology.............................................................. 5 Hydrology ................................................................ 5 Surface water.......................................................... 5 Surface-water quality.................................................... 8 Ground water.......................................................... 8 Ground-water quality.................................................... 12 Drinking water............................................................. 12 Present drinking-water supplies ........................................... 12 Quality of present supplies ............................................... 13 Alternative drinking-water sources......................................... 13 Summary ................................................................. 13 References cited............................................................ 14 Appendix 1. Water-quality records for North Fork Chester Creek and drains near the Merrill Field airport. .............................................. A-l Appendix 2. Well inventory and water-quality data for wells in the Merrill Field airport area A-13 FIGURES 1-4. Maps showing: 1. Location of Merrill Field Airport, Anchorage, Alaska..................... 2 2. Chester Creek drainage basin........................................ 6 3. Five-year average, mean daily discharge for Chester Creek at Arctic Boulevard, Anchorage for water years 1989-93 ................................... 7 4. Location of observation wells and geologic section through wetlands and the landfill ................................................... 11 TABLES 1. Mean monthly temperature, precipitation, and snowfall for the period 1952 to 1987, Anchorage International Airport, Anchorage, Alaska ............. 4 2. Information on wells in the Merrill Field airport area......................... 10 3. Wells near the Merrill Field airport area in which water sample concentrations exceeded drinking-water regulations.......................... 12 Contents III CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS Multiply By To obtain millimeter (mm) 0.03937 inch meter (m) 3.281 foot kilometer (km) 0.6214 mile hectare (ha) 2.471 acres square kilometer (km2) 0.3861 square mile meter per day (m/d) 3.281 foot per day liter per day (L/d) 0.2642 gallon per day cubic meter per second (m3/s) 35.31 cubic foot per second degree Celsius (°C) °F = 1.8 x °C + 32 degree Fahrenheit (°F) Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929~a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. IV Contents Overview of Environmental and Hydrogeologic Conditions at Merrill Field Airport, Anchorage, Alaska by Allan S. Nakanishi Abstract The Federal Aviation Administration (FAA) operates facilities on or near Merrill Field airport in the Municipality of Anchorage, Alaska. The airport is surrounded by developed urban areas and up to 80 percent of the land surface is covered by asphalt, concrete, build­ ings, or other impervious surfaces. The airport area is underlain by unconsolidated glacial, alluvial, estuarine deposits, weakly lithified sedimentary rocks, and a large landfill. Ground water is available from both unconfined and confined aquifers within the unconsolidated deposits; however, most residential, commercial, and industrial consumers in the area obtain water from the municipal water-supply system. INTRODUCTION The Federal Aviation Administration (FAA) owns and (or) operates airway support and nav­ igational facilities throughout Alaska. At many of these sites, fuels and potentially hazardous mate­ rials such as solvents, polychlorinated biphenyls, and pesticides may have been used and (or) disposed of. To determine if environmentally hazardous materials have been spilled or disposed of at the sites, the FAA is conducting environmental studies mandated under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or "Superfund Act") and the Resource Conservation and Recovery Act (RCRA). To complete these more comprehensive environmental studies, the FAA requires information on the hydrology and geology of areas sur­ rounding the sites. This report, the product of compilation, review, and summary of existing hydro- logic and geologic data by the U.S. Geological Survey, in cooperation with the FAA, provides such information for the FAA facilities at Merrill Field Airport and nearby areas in Anchorage, Alaska. BACKGROUND Location and History Anchorage is in south-central Alaska and had a population of approximately 240,000 in 1990, which was approximately 50 percent of the total State population (Alaska Department of Commu­ nity and Regional Affairs, 1993). An area known locally as the "Anchorage Bowl" or the "Bowl," encompassing an area of approximately 470 km2 (fig. 1), is bounded on the west by Cook Inlet, on the north by Knik Arm, on the east by the Chugach Mountains, and on the south by Turnagain Arm. The Merrill Field FAA facilities, on Merrill Field municipal airport, is in the Municipality of Anchorage at about lat 61° 12' N. and long 149°50' W. INTRODUCTION 1 61° 15' 61° 05' Figure 1. Location of Merrill Field Airport, Anchorage, Alaska. 2 Overview of Environmental and Hydrogeologic Conditions at Merrill Field Airport, Anchorage, Alaska In the 1940's, Merrill Field airport was constructed on what was then the outskirts of Anchor­ age. Along the southeast side of the airport was a bluff that overlooked North Fork Chester Creek and below the bluff were wetlands (Brunett, 1990). The Merrill Field solid-waste landfill was cre­ ated in the 1940's by dumping refuse off the bluff near the east end of the Merrill Field Airport runway. When the landfill was closed in 1987, approximately 80 ha of the original wetlands had been covered with soil and refuse to an average thickness of about 10m. Merrill Field FAA Facilities The FAA owns and operates a flight service station (FSS), air traffic control tower (ATCT), visual approach slope indicators (VASI), and runway end identification lights (REIL) on Merrill Field airport (Ecology and Environment Inc., 1994). Approximately 30 FAA personnel operate and maintain the FAA facilities at Merrill Field airport. A detailed description of FAA facilities near Merrill Field and an investigation of potential sources of contamination is included in a report by Ecology and Environment, Inc. (1994). PHYSICAL SETTING Climate Anchorage is located in a transitional climate zone, situated between maritime and continen­ tal climate zones. Seasonal precipitation patterns in this zone are not sharply defined, fluctuate from year to year, and may resemble those of either the maritime or continental climate zones (Hartman and Johnson, 1984). The mean annual temperature for Anchorage at the Anchorage International Airport (AIA), about 8 km southwest of the Merrill Field airport, is 2.1 °C, but temperatures range from a July mean maximum of 18.3 °C to a January mean minimum of about -13.2 °C. Precipita­ tion increases with increasing elevation eastward toward the Chugach Mountains (Patrick and oth­ ers, 1989). Mean annual precipitation at the AIA is about 390 mm and mean annual snowfall is approximately 1,760 mm (Leslie, 1989). Most rainfall occurs from July through October. Mean monthly temperature, precipitation, and snowfall for the weather station at the AIA are summa­ rized in table 1. Vegetation Selkregg and others (1972) provide a map and description of vegetation types in the Anchor­ age area. Vegetation near the Merrill Field airport generally includes four groups: interior forest, treeless bogs, spruce bogs, and developed areas. The interior forest is predominantly found on well-drained hills east of the Merrill Field airport. Tree species typical of the interior forest include white spruce, paper birch, balsam poplar, black cotton wood, and willow (Viereck and Little, 1972). Shrubs in the interior forest include wild rose, lingonberry, bunchberry, currant, and Labrador tea. Treeless bogs are found in poorly drained, flat areas north, east, and south of the airport where soils are too water saturated